Process of making air-cooled cylinders



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15 25 #2 Zarneys Patented May 1, 1928.

UNITED STATES PATENT OFFICE.

CHARLES F. KETTERING, OF DAYTON, OHIO, ASSIGNOR TO GENERAL MOTORS BI-SEARCH CORPORATION, OF DAYTON, OHIO, A CORPORATION OF DELAWARE.

PROCESS OF MAKING AIR-COOLED CYLINDERS.

Original application filed November 9, 1921, Serial No. 514,014. Dividedand this application filed. October 29, 1923. Serial No. 671,490.

This invention relates to the manufacture of products composed ofdifferent metals integrally bonded together, and more particularly tothe manufacture of air-cooled cylinders for internal-combustion enginesor the like, wherein heat-dissipating elements of a relatively highheat-conducting metal are caused to cohere to ferrous or other metalliccylinders of relatively low heat conductivity,

thus forming an integral heat-transfer unit of high efiiciency.

This application is a division of application Serial No. 514,014, forinternal-combustion engines, filed Nov. 9, 1921, which is a continuationin part of application Serial No. 392,646, filed June 29, 1920.

Objects of the invention are the production of an air-cooled enginecylinder having heat-dissipating elements composed of a metal of higherheat conductivity than the cylinder, integrally bonded to the cylinderin a manner to provide a continuous molecular path of metal to conductheat from the cylinder into the heat-dissipating elements;

the production of a cylinder or the like, having said heat-dissipatingelements formed as part of a continuous sheet of high heatconductingmetal integrally bonded to the cylinder: and the formation of suchcylinders with heat-dissipating elements of extensive surface and thelargest and easiest path practicable for conducting heat from thecylinder.

The invention consists in the process, hereinaftcr described andclaimed, whereby heat-dissipating elements of small thickness and largeheat-dissipating area may be intcgrally bonded to a body of relativelylow heat. conductivity, in such manner as to proride an extensiveuninterrupted molecular path of metal for the free conduction of heatbetween the said body and said elements.

In the accompanying drawings, in which like reference charactersindicate like parts throughout the several views;-

Fig. 1 is a perspective view illustrating the method of assembling acontinuous strip of finning material and a brazing material around acylinder.

is a side view showing the heatdlsslpating or finning structure clampedto a cylinder ready for the furnace;

Fig. 3 is an enlarged cross section of a fragment on the line 33 of Fig.2;

Fig. 4 is a diagrammatic view showing the operation of a machine whichpleats or folds a thin metallic sheet to make a strip of finningstructure;

t Fig. 5 shows one form of the finning strucure;

Fig. 6 is a cross sectional view taken through a cylinder made inaccordance with the invention;

Fig. 7 shows the completed cylinder and 65 part of a tube surroundingthe finning strucure;

Fig. 8 is an enlarged view of a diagrammatic and exaggerated nature,showing in cross-section the bond between the finning structure and thecylinder wall;

Fig. 9 is a plan view partly in section of an engine made in accordancewith "the invention;

Fig. 10 is a side view of the engine shown in Fig. 9 partly in section.

The construction of engine and engine cylinder willbest be understood byfirst describing the structure of the heat-dissipating elements or finsand cylinder shell and then the method of attaching the fins to thecylinder shell. For the purpose of comprehending more clearly thedescription which follows, reference should be had to Figs. 1, 2 and 3of the drawings, which show the heat 85 dissipating or firming structure31 and the cylinder shell 30, to which said finning structure is to beattached, said shell having a flange 30 by which it may be secured to abase such as an engine crank case.

In order to facilitate the attachmentof the fins to the shell, to secureuniformity of attachment, to save labor and secure other advantages, Iprefer to form some or all of the fins of a strip of copper or otherhigh heat-conducting metal, bent or crimped to the shape of the fins,and in the embodiment here illustrated I have shown all the fins madefrom a continuous thin strip of metal so that there will be a largenumber of fins 100 which will be attached to the cylinder simultaneouslyand under uniform treatment; that is, each fin is subjected tosubstantially the same condition as all the other fins in the process ofattaching the fins to the shell. These fins may be made of substantiallypure metallic copper which is preferably of umform gauge, and while thethickness of the copper depends upon the type of engine upon which it isemployed and other factors, I prefer for installation on the engine ofan ordinary passenger car, to use a thin sheet of copper. In actualpractice, copper strips ranging from thirteen to eighteen thou sandthsof an inch have given good results in automobile engines.

The heat-dissipating or finning structure illustrated in Figs. 1, 2, 3,6 and 7 provides a number of uniform radial fins spaced equidistant andarranged with their outer edges concentric with the peripher of theshell; for convenience, this type of finning structure will be, referredto hereinafter as concentric finning. The fins need not be uniform,however, and in another form of the invention which is illustrated inFigs. 5, 9 and 10, the cylinder is provided with fins of varyin height(that is, radial extent beyond the cylinder shell) in order thatcylinders of an engine may be placed more closely to ether and space beprovided for certain of the Working members such as valve push rodswhich would otherwise be obstructed by the finsthe finning structure,when assembled on the cylinder, may present an external configurationwhich is eccentric with respect to the periphery of the shell,notwithstanding the fact that the bases of the fins are concentric withand attached to the shell. The invention will first be described withreference to the attachment of an externally concentric finningstructure to the shell, and thereafter with reference to the attachmentof a finning structure which is not externally concentric.

Referring first to Figs. 1, 2, 3, 6 and 7, it will be seen that thefinning structure con sists of a plurality of fin loops, 32, each loopincluding two fin portions 320 exposed on both sides to cooling air, andof base portions 33 connecting the loops 32. The distance from the baseof a fin to the outer edge of the fin, is hereinafter referred to as theheight of the fin, and the distance from the top edge of the fin to thebottom edge of the fin in a longitudinal direction being referred to asthe length of the fin. By referring to Fig. 3, it will be noticed thatthe fins are shorter than the length of the cylinder and it is desiredto have them embrace the cylinder more particularly around the upperzone of the cylinder which becomes hottest in the operation of theengine. By curving the fins circumferentially around the cylindeain themanner illustrated in Fig. 1, it

will be noticed with reference to Fig. 3, that the bases of successivefins are contiguous to each other, thus forming approximately a circularcylinder, and the flexibility of the.

metal sheet is such that the base ortions 33 can conform to theperiphery 01 the cylinder when the fins are pressed against the cylindershell in the manner more particularly hereinafter described. It willthus be obvious that the bases 33 of the fins, edge to edge, at this stae in the process of manufacture, form a su bstantially circularcylindrica'l surface broken at the points where fins 320 formed by thesides of the loops 32 extend outwardly from the bases thereof. Theprovision of these bases of relatively large area is important becauseit insures good face contact between the base of the finning structureand the bonding metal as hereinafter described, thus providing a maximumsurface for attachment and insuring both mechanical strength andeflicient heatconducting capacity.

The process of attaching the finning structure to the shell may forpurpose of convenience be divided into a number of steps although itwill be obvious that some 0 these steps may be combined and modifiedwithout departing from the invention. The preferred process of theinvention involves 1. Forming the finning structure.

2. Preparing the finning structure for fiuxing.

3. Fluxing the finning structure.

4. Preparing the cylinder for fluxing.

5. Fluxing the cylinder shell.

6. Assembling the fins, bonding metal, and cylinder.

7. Fluxing the assembly.

8. Brazing operation.

9. Removal of flux and finishing.

I will now proceed to describe the preferred process of manufacture stepby step including the brazing operation both in a gas furnace and in anelectrical furnace, both of which have been employed with success. Amachine for manufacturing the finning structure forms the subject matterof patent to C. L. Lee, No. 1,507,318, and in itself is no part of thepresent invention except in so far as it is used in the process ofmanufacturing engine cylinders in accordance with the present invention.

1. Forming the finning stmw't'wre.

In order that the formation of the sheet copper into the finningstructure may be better understood, the operation of the machinereferred to is illustrated diagrammatically in Fig. 4. The copperemployed is preferably pure, and in practice I prefer to use a sheetcopper which is 99.85% pure copper. Care should be taken that the copperis of uniform gauge, so that when the predetermined number of fins havebeen 1,ees,bos

formed, the finning structure will be exactly the correct dimensions toextend substantially exactly around the cylinder.

In Fig. 4 the sheet metal is indicated at.

40 and is shown as having been formed into a series of folds indicatedat 41. The metal will be supplied from a suitable roll which in thepresent form of machine is supported by some exterior roll holder (notshown) and is fed from the right hand of this mechanism through guides42, under the grip or clamp 43 under the head of the ram 44, and asindicated, over the apron or platform 45.

When the machine is in operation, the matrix 46, occupies the positionshown in this figure, being secured in place against the top plate 47,by means of the clamp 48, and as the ram 44 moves over the apron 45,towards matrix 46, the grips upon the ram fasten upon the sheet 40 andcause it to buckle between the face of the ram and the matrix 46whereupon the base forming element 49 is lifted to the position shown toallow the small bead 50 to project up above the upper plane of the apron45 and come between the matrix 46 and the face of the ram, in order toform the base portion 33 connecting the folds. By the time the baseforming element 49 has been lifted into position, the face of the ramforces the sheet of metal against the matrix 46 and the bead 50, forminga fold such as indicated at 41.

As soon as the ram starts upon its first return or releasing movementthe base forming element 49 drops below the apron 45. The rain thenmoves forward to complete the forming of the fold, after which itreturns to its original or outermost position. A second matrix, of thesame contour as the first matrix 46, moves forward and slides in frontof the first matrix and the newly formed fold. Before the second matrixhas completed its travel in front of the first matrix, the clamp 48operates to release this first matrix and these two matrices move to theleft a distance of the width of a fold, carrying therewith the sheetmaterial and folds. The second matrix then completes its movement infront of the first matrix, occupying the former position of matrix 46 sothat the ram may repeat its operation on the material to form anotherfold.

"When a suitable number of folds have been formed by theseveraloperations just described, the strip is cut by means of a knifeillustrated at 51.

2. Preparing the flaming structure for flaming.

After the finished strip of fins has been cut off to the proper lengthand leaves the -firming machine, it is cleaned preferably by toneutralize the nitric acid: then washing it with a brush and thendipping it in hot water. The fins are then ready for the first fluxingoperation. The various steps of cleaning and dipping to which this stripof fins is subjected after it leaves the finning machine may be modifiedin a manner obvious to those skilled in the art, the purpose of thistreatment being to get the copper fins in the desired clean conditionfor securing the most satisfactory bond between the copper and the othermetals in the brazing operation.

3. Flaming the finm'ng structure.

A suitable flux is applied by a brush or other suitable means on theunder surface of the bases 33 of the fins, which surface comes intocontact with the brass used in the brazing operation. The flux which hasbeen found to give the best results in practice consists of a mixture ofborax and boric acid. It is preferred to use a composition composed ofone part by weight of borax, one part by weight of boric acid and eightparts by weight of water. The flux is applied hot and preferably at atemperature of about boiling point. Care should be taken not to use toothick a flux. The flux should also be uniformly applied, and by applyingit in liquid form, it is evenly distributed on the surface of the metal,thereby assisting in securing a uniform bonding. The flux may bepermitted to dry, or specially dried prior to the assembling. In orderto distinguish this fluxing operation of the fins from a second fiuxingoperation hereinafter described, this operation may be referred to asthe first fluxing, and the flux employed may be referred to as the thinflux in order to distinguish it from the flux used in the second orheavy fluxing.

4. Preparing the cylinder for fluwing.

' The iron cylinder to which the copper fins are to be attached is madeby the usual casting operation or in any other suitable way and theouter face of the cylinder is given a smooth finish, as by grinding,cutting or any other suitable operation which will remove anyobstructions or scale on the outer face of the cylinder, and will giveit an even bearing surface for the brazing metal and fins when appliedas hereinafter described. It has been found advantageous after thissurface has been thus prepared. to electroplate the outer surface of theengine cylinder with copper (usually a light coating) whichelectroplating is done in any usual manner. In addition to otherdesirable effects, this plating prevents oxidation of the outer surfaceof the engine cylinder, so that if a considerable period of time elapsesbetween the time when the cylinder is conditioned for assemblage, andthe actual as- Sembling operation, there is no problempf; removingoxidation as would be the case with a cylinder not provided with thlsprotecting coating of electroplated copper.

6. Flaming the cylinder shell.

' suitable flux, which is preferably the same kind of flux, (viz, a thinflux) that is used on the surface of the bases 33 of the fins anddescribed above with reference to the fluxing of the finning structure.This flux is also permitted to dry or suitably dried prlor to theassembling operation.

6'. Assembling operation.

As illustrated in Fig. 1, after the shell has been thus prepared, it isready to be assembled with the bonding metal, which is shown as asheetor band of brazing brass or solder 34, and the sheet of fins 31. Itwill be seen that the thin fluxing hereinbefore described provides alayer of flux between the copper of the fins and the brazing solder 34,and between this band 34 and the outer surface of the engine cylinder.If desired, the flux might be applied on both sides of the brazingsolder, but it is preferred to apply it on the cylinder and fins asbefore described.

The brazing solder 34 is in the form of a band, which is bentcircumferentially around the cylinder, so that its two ends cometogether in proper position, and this preferably slightly overlapping.When sheet brass or brazing solder is employed as herein described, ithas been found that the best results are obtained by using a. brazingsolder which contains about 62% of copper. This permits of heating thesolder by a brazing heat which should not be so hot as to damage the finas would be the case where the melting point of the solder is too high.I do not limit myself, however, to the use of brass as a bonding metal,nor to a brass having the percentage of copper recited above. Silversolder can be employed to get good results as a bonding metal. It isimportant that the bonding metal selected should not have a meltingpoint so high that in order to bring it into condition to form theproper bond, the assembly has to be heated so highly as to melt thecopper of the fins. It is preferred to use a thin sheet of brass orother bonding metal and good results have been obtained by using a sheetin the neighborhood of 7 to 8.thousandths of an inch in thickness.

Around the sheet of solder is then placed the finning structure and theassembly secured in any suitable manner as by wires 35. In constructinga cylinder for an engine, the stroke of which is three and one halfinches and the bore of the cylinder three and one half inches, it hasbeen found satisfactory to use about five pieces of wire. This wire ispreferably made of basic iron and good results have been obtained. inthe use of an iron wire about .078 of an inch thick. With largecylinders, it is preferred to use a heavier gauge of wire. The functionof this wire is not merely to hold the assemblage in position during theheat-treating operation which follows, but it also serves as a pressuremeans to force the copper and brazing solder against the shell duringthe heat operation owing to the difference in the coefficient ofexpansion of the metal of the wire and the other metals of the assembly.Inasmuch as the heattreatment causes an expansion of the copper finningwhich is resisted by the wire,,the copper finning is forced against thebrazing strip and the cylinder wall in the heat-treating operation.

7'. Flaming the assembly.

The assembly is now ready for what may be termed the second fluxingoperation or thick fluxing, which consists in coating all the exposedsurfaces of the copper fins with a heavy fiux. Any suitable flux may beused, and the purpose of this flux is to protect the copper againstundergoing changes in its physical condition during the brazingoperation. It has been found that by the use of a flux of borax andboric acid, the copper fins, after they leave the furnace are inexcellent condition and have not deteriorated, become burned, oxidizedor brittle as a result of the heat to which they have been subjected.The use of such flux is particularly important in case there should be areducing atmosphere in the furnace, which would tend to render thecopper brittle. The preferred form of flux consists of a mixture ofborax and boric acid in equal parts by weight diluted by water until themixture has a specific gravity of about 1.300 at a temperature of 180 F.Care should be taken to maintain the flux at this temperature, becauseif it cools to any great extent, the ingredients settle out and becomeset and the flux cannot be used; therefore, once it has been made up, itshould be maintained at the right temperature. Into this flux, theassembly is dipped, after which it is allowed to dry. The thickness ofthe flux may be varied depending upon the type of furnace employed.Where the furnace does not have a reducing or oxidizing atmosphere, thecoating of flux need not be so heavy.

8. Brazing operation.

The heat treatment necessary to fuse the other heating apparatus whereproducts of combustion may be kept from the assembly, because it isparticularly important that no products of combustion come in contactwith the thin linning structure and the joint between it and thecylinder to which it is to be attached. Carrying out the bondingoperation in an electric furnace has the advantage that temperatures canbe more uniformly controlled than in a gas furnace; there are noproducts of combustion to interfere with the bonding operation; and theheat applied is radiant. A furnace which has been most successfully usedin carrying out the process is one that is known in the trade as theHoskins type FB #206 Hairpin resistor furnace.

During the heat treatment, the assembly should be maintained in positionwith the axis of the cylinder horizontal, and should be continuouslyrotated during the heat treatment and the rotation continued duringcooling.

The heat treatment may be applied in a rotary furnace of the typedescribed in patent to C. L. Lee, No. 1,445,220. In this furnace,products of combustion are substantially prevented from coming intocontact with the finning structure and the exterior of the cylinderShould any small quantity of combustion gases escape into the atmospheresurrounding the assembly, they cannot produce any deleterious effectupon the thin finning structure because the exposed surfaces of saidstructure are coated with a protective flux, nor for the same reason,can the structure become oxidized.

It is desired to heat the assembly to a temperature at which the brazingsolder will be in sufficiently fluid condition to flow into all thespaces between the fin structure and the iron cylinder shell, thereby toassist in forming a strong union with the adjacent copper and iron afterthe assembly has cooled. It is preferred to heat the assembly until itreaches a temperature at which the brazing solder will be in a liquidcondition. This will be at a temperature above the melting point of thesolder, but care should be exercised not to heat the assembly to atemperature at which the copper will begin to melt. Vhere the brazingsolder contains in the neighborhood of 62% and 63% copper, I find thatwith a cylinder, brazing solder sheet, and finning of the dimensions andmaterials specifically referred to herein, good results are obtained byheating the assemblyto a point where the temperature in the neighborhoodof the union of the fins with the cylinder is about 17 25 F. Thistemperature may be referred to as the final temperature, and when it isreached, the heat of the furnace is shut oif, as the brazing solder atthis temperature will be in the proper fluid condition, so that aftercooling a satisfactory union will be effected between the copper finningand the cylinder. It will be understood that the final temperature ofthis furnace will depend upon the bonding material employed, as well asupon other factors. Where silver solder is employed as the bondingmaterial, as described later, the final temperature will be lower. iVhenthe brazing solder is in a fluid condition, it alloys with, orintermingles with, the copper of the fin structure, and also alloys withor intermingles with, or penetrates into the iron. \Vhile the specifictemperatures herein referred to have given good results in a furnace ofthe type described, it will be understood that these temperatures mayvary.

The assembly may be maintained at the final temperature or at a pointapproximately the final temperature for as long as desired, but in suchcase the brazing must take place in a furnace in which the heat will notrise above the predetermined point, otherwise the cylinder will beoverheated.

Owing to the fact that the brazing solder is brought to a fluidcondition in the brazing operation, it becomes necessary to providemeans for preventing the solder from flowing away from its positionbetween the finning structure and the shell. It is also desirable toprovide means for insuring an even distribution of heat throughout thewalls of the engine cylinder. In the preferred form of the presentinvention the cylinder is inserted in the furnace with its axishorizontal, and the cylinder is rotated,

oscillated, or otherwise moved in such a way that the tendency of thesolder to flow out of its interposed position under gravity is resisted.This rotation of the assembly also insures an even distribution of thebrazing solder between the shell and the fins when the solder is influid condition. The rotation or other movement imparted to the assemblyshould be continued during the brazing operation and the subsequentcooling operation until the brazing solder sets. The rotation of thecylinder prior to the melting and flowing of the brazing solder, as wellas thereafter, insures that each and every part of the wall of thecylinder is subjected to substantially uniform heating in the furnace,notwithstanding the possibility of uneven temperature zones existingwithin the furnace. It is preferred that the rotation of the assemblyshould be relatively slow and in the practice heretofore followed theassembly has been rotated at a speed of about 16 to 18 revolutions perminute.

In the case of a gray iron cylinder of the dimensions hereinbeforereferred to having a wall about 9/32 of an inch thick using copperfinning fifteen thousandths of an inch thick, and a sheet of brass(62.5% copper) seven thousandths of an inch thick, it has been foundthat good results are obtained Ill) when the cylinder stays in thefurnace about 14 minutes before reaching the final temperature, andduring this period, the furnace should be rotated at a speed of about 16to 18 revolutions per minute. The thick flux on the fins protects themfrom oxidation, notwithstandin the fact that the entire assembly isbroug t up to bright red heat.

Examination of the assembly during the heat treatment shows that thecopper fins expend to such an extent that each fin bows or endsoutwardly putting pressure on the bonding surface, and as the iron wires35 are in contact with the outer surface of the fins along awell-distributed area, the base 33 of each fin is pressed firmly andwith even pressure against the cylinder wall. The cylinder is allowed tocool slowly within the furnace without free access of air to the finswhile rotating as hereinbefore described, after which it is cooled inthe air.

9. Removal of flux and finishing.

The flux is removed in any suitable manner, for instance by boiling in asolution of so-called Edis compound after which it is dipped in a nitricacid bath to remove General considerations.

It will be appreciated from the above description of the brazingoperation that the temperature conditions must be such that the brass isbrought into the best condition for forming a bond with the cast ironand the copper fins, and that care should be taken that this bond shallbe as uniform as possible, and should extend over substantia ly theentire area of the under surface of the finning structure. By conductingthe heat operation in the manner described, sulficient heat is appliedto bring the assembly up to the desired temperature, and sufiicient timeis given to enable the metals to become uniformly heated and bonded. Themolten brazing solder unites with and coheres to the copper of the fins,and the iron is united with the contiguous metals which adhere to it.

Attempts have been made to shear off the I metals of the union from acylinder made in accordance with the process, and it has been found thatthe contiguous metals are bonded to the iron with a strength greaterthan the breaking strength of the contiguous brass and copper indicatingthe presence of a zone of cohesion intermediate the iron and thecontiguous metals where the iron is combined or alloyed with thecontiguous metals.

Examination of the union under a micro scope indicates that any thincopper electroplatingthat may have been on the outside of the cylinderis absorbed by the molten brass.

completed structure.

A magnified cross section of the union between the cylinder and a fin isillustrated in Fig. 8, in which 145 represents the cast iron cylinderand 146 represents the zone of intermixture, alloying or cohesionbetween the iron and the brazing solder, 147 represents the zone ofsolder, 148 represents the zone of intermingling, alloying or cohesionbetween the solder and the copper of the finning structure, and 149represents the substantially pure copper. The zones 146 and 148, arerepresented diagrammatically by the symbol mama: and may not be asthick, relatively, as the drawing indicates. So far as I am able toascertain these zones are present in the But the dimensions andthicknesses are exaggerated for the sake of clearness, and are notintended to be accurately proportional. Microphotographs of sections ofbonds produced by the hereindescribed process indicate that there is aprogressive merging metallic path for the condition of heat from theiron to the cooper,

and tests tend to show that true thermal connection exists between thefins and the iron. At least this union offers considerably lessresistance to the passage of heat than would be the case in a junctionwhere the copper fins are merely in contact with or adhesively held tothe iron.

It will be noted from examination of Fig. 8 that the brazing solder hasflown up between the edges of adjacent fins during the brazing operationas indicated at 150 bonding these fins together, thus strengthening theroots of adjacent fins. The bases of adjacent fins are thus eachinterconnected by the brazing solder alloyed therewith so that there isformed a continuous skin of heat conducting metal around the outside ofthe cylinder from which the roots 321 of the fins project and mergeintothe fins proper, the roots of these fins being preferably of greaterthickness than double the thickness of the fins beyond the roots.

While it is desirable to have a continuous skin on the outside of thecylinder, as described above, as it permits of equalizing thedistribution of heat in the outer surface of the cylinder, the inventionis not limited to a bond between the fin and the engine cylinder whichresults in the formation of a skin, 'as each fin might be affixed by abond of the type described above without contacting with the adjacentfins. Moreover the contact between each fin and the engine cylinder maybe and preferably is continuous, it may also be a series of shortcontacts. It will be noticed that the flow of heat takes place veryreadily from the inside of the cylinder shell to the fins; a relativelythin iron shell is preferably used, and the heat passes rapidly to thebond and passes relatively unimpeded over the zones 146, 147 and 148into the copper 149 of the fins which are usually subjected to coolingair as hereinbefore described. The melting point of the brazing metalbeing higher than that attained in the normal operation of the engine,there Will be no tendency for the fins to come off the cylinder in theoperation of the engine due to the heat of engine operation, and testsextending over a considerable period indicate that no deterioratingaction tending to weaken the bond takes place after rapid running oftheengine for a considerable length of time, so that the attachment of thefins to the cylinder may be termed a permanent one. It will be foundthat the union between the fins and the engine cylinder is continuousnot only circumferentially between adjacent fins, but alsolongitudinally between the shell and the fin. The mechanical strength ofthis union is such that if it is attempted to pull the fins off thecylinder of the dimensions heretofore described, they will break at apoint in the copper and not at the point of junction.

Notwithstanding the fact that the cast iron is heated to a hightemperature, it is not injured by the brazing operation. It will furtherbe noticed that a large number of copper fins are employed, and thatthese fins are made of relatively thin copper; each fin is permanentlyattached to the cast iron cylinder by the intermediary of a heatconducting union which covers an extensive area of the cylinder comparedwith the cross sectional area of the fin.

Good results have been obtained by the use of a fin in which the heightof the fin is in the neighborhood of about times the thickness of themetal of the fin; the total number of fins employed and their height andlength and distance apart are also preferably predetermined with theView of providing a very extensive heat dissipating surface. Thisextensive heat dissipating surface is obtained by employing a largenumber of thin copper fins separated by relatively small air spaces. Inthe embodiment of the invention shown in Fig. 6, sixty fin loops 32,providing in all one hundred and twenty fins 320 are shown. In practiceit has been found advantageous to use about 12 fins per peripheral inch.

While the union of metals in accordance with the invention may beemployed with any thickness of copper fins, I prefer nevertheless to useit with a thin fin such as described herein and having the advantagesreferred to.

It will be noted by examination of the strip of finning illustrated inFigs. 1 and 3 that the fins are equidistantly separated and are foldedso as to have the inner edges provided with a flat baseproduced byflaring the inner portions of the several folds or crimps as clearlyshown. This form of fin,

which may be termed afiare edge or baseformed fin, has been found tohave decided advantages. It assists in uniformly spacing the fins apart,and it provides for more equal distribution of the air between the fins.

The preferred form of fin or cooling element consists of a fold or finloop of sheet metal forming a flattened tube having one edge attached tothe cylinder wall. This tube is open at both ends and allows the passagethcrethrough of a draft of air, while an additional draft of air iscaused to pass along the outside of the several fins by surrounding theentire fin structure with a sleeve indicated at 155.. (Figs. 6 and 7.)

Referring to Figs. 9 and 10 which show a portion of a complete engine156, it will be noticed that the cylinders 157 and finning 158 aresurrounded by the draft tube 159 which merges into a head portion 160leading into the inlet side of a fan 161 driven by the engine. Becauseof the large area of the heat dissipating fins, an eflicient cooling ofthe engine takes place with the utilization of a fan which takes only asmall proportion of power from the engine in order to provide a flow ofcooling air sufficient to keep the cylinder efficiently cooled. It willbe observed that while the present process may be employed for bondingsingle fins, sections of fins, or all the fins simultaneously in asingle operation, there is an advantage in bonding a complete finningstructure to the cylinder in a single bonding operation, not onlybecause it is .more economical, but also because each fin is attached tothe cylinder by substantially the same amount and thickness of bondingmetals and the same kind of bond made under the same conditions as itsneighbors, in other words, there will be substantial uniformity in theattachment of the fins and this makes for uniformity in the flow of heatinto the fin in the running of the engine. I will also be noted that theattachment of the fins does not call for exceptionally skilled manualoperations, so that the completed cylinders may be made in a factoryunder quantity production conditions such as exist in the automobileindustry.

Silver solder process.

Instead of attaching the fins by brazing solder, as described above, Isometimes employ silver solder which also produces advantageous resultsin forming a union of the metals which will be satisfactory in practice.The process employed is, in the main, the same as that described above,the silver solder being used in the form of a band similar to thebrazing solder band 3%. The melting point of the silver solder, however,being less than the melting point of the brazing solder, the brazingoperation in lll) Attacking fiais to steel cylinders.

The process of the invention as described above may be applied equallyto the manufacture of a steel cylinder having copper fins attachedthereto. The process for attaching copper fins for a copper finningstructure to the steel cylinder is substantially the same as thatdescribed above with reference to cast iron cylinders. When the cylinderis made of steel it can be made much thinner than cast iron. For acylinder having a bore of 3-1/2 inches and a stroke of 3-1/2 inches asuitable wall thickness will be about 5/64 of an inch.

Examination of the union between the steel and the copper fins showsthat it has the same characteristics as the union between the cast ironcylinder and the copper fins and the cylinder presents similar desirablequalities in use.

E ccent rz'c finning process.

The invention has been described above with reference to fins arrangedconcentrically around the engine cylinder, each fin being of the samedimensions as its neighbor. In constructing an engine utilizingcylinders in accordance with the present invention, it is found possibleto reduce the length of the engine by arranging the cylinders in' pairswith the inlet sides of the cylinders closer together than the outletsides. Such an arran ement is shown in Fig. 9, wherein the in ct portsof the cylinder 157 are indicated at 162 and the exhaust ports 163. Thevalve structure is omitted in Fig. 9 for sake of clearness.

It has been found that the fins at the inlet sides of the cylinder neednot provide so large a conducting area and so large a. heat dissipatingarea as the fins on the outlet side of the cylinder, inasmuch as theinlet side of the cylinder is cooled b the incoming fuel mixture whilethe ex aust side of the cylinder is heated by the outgoing products ofcombustion. It thus becomes desirable to provide fins of a varyingcontour, which contour may be that indicated in Fig. 5, which shows anend elevation of the so-called eccentric finning structure 170 in thecondition in which it leaves the finning machine, there being provided aseries of short fins 171 to permit the cylinders to come close together,which short fins are located on the inlet side of the cylinder. Theshort fins 172 provide passage for the push rods for the valves. Thefins 173 are shortened to reduce the distance between the adjacent pairsof cylinders. Such a finning structure may be assembled in the samemanner as that above described for fins of even height and suitablespacing blocks provided to fill out to circular outline the assemblywhich may then be wired as before.

7 Stress is laid upon the desirability of ap plying even pressure toeach of the fins, and causing even contact of each fin with the bondingmaterial because the successful adhesion between the fin and thecylinder depznds to a considerable extent upon the fin ing pressed intocontact with the cylinder by the wire during the heating.

While there has been described specifically a method of brazing copperfins of a particular form to a cast iron or steel cylinder, it is to beunderstood that the invention is not limited to these specific formsherein, which are the preferred ones and have given satisfactory resultsin practice. The examples of dimensions herein referred to, togetherwith the specific types of apparatus employed are given herein by way ofreference or examples, and not by way of imitation, as I believe it isnovel in this art to attach a fin of copper to a cast iron, steel orother type of cylinder by a metallic union which is permanent, ivesexcellent thermal contact, is mechanica ly strong, and

does not deteriorate substantially under running temperatures andrunning condi-,

tions of an internal combustion engine. The heat from the cylinderpasses throu h the union from the iron to the copper wit out substantialobstruction, and the fin, being made of copper (which is almost ninetimes as good a conductor as iron), rapidly draws the heat out of thecylinder. This heat is withdrawn from the copper fins by the cooling airstream, and, owing to the large number of copper fins and theirrelatively large dimensions, the engine cylinder has a very large heatdissipating surface which increasesdts cooling efliciency to a markeddegree as compared with the iron or steel fins common in this art.

The invention may also be found useful in connection with the brazing ofcopper and any heat exchange vessels which are subjected to conditionssimilar to those obtained in the interior of an engine. The term brazingmetal as used in certain of the appended claims is intended to mean notonly brass of a specific composition such as herein given, but any alloyor metal which can act in the same way as brass in effecting a unionbetween the shell and the fins, which fins are not necessarily made ofcopper as Jun I fins, itis to be understood that it may apply to, and beemployed equally advantageously in attaching fins of other suitable highconductive metals to the engine cylinder. and that while the enginecylinder is here described as being made of cast iron or steel, it maybe made of other suitable metal without departing from the bounds of myinvention, or the scope of the annexed claims.

The processes, ap aratus and article herein shown and descri edconstitute preferred embodiments of the invention, but it is to beunderstood that other forms might be adopted and changes made, allcoming within the scope of the claims which follow.

What is claimed is as follows:

1. The process of bonding a non-ferrous metallic structure of high heatconductivity to a ferrous body, which consists in assent bling thenon-ferrous structure and the terrous body with a layer of suitablebonding metal and suitable flux interposed between said structure andsaid body; coating the non-ferrous structure with a protective layer offlux. then heating the assembly to a red heat with the non-ferrousstructure and adjacent surface of the body free from contact withproducts of combustion.

2. The process of bonding a non-ferrous metallic structure of high heatconductivity to a ferrous body, which consists in assembling thenon-ferrous structure and the ferrous body with a layer of suitablebonding metal and suitable flux interposed between said structure andsaid body; dipping the entire assembly in a bath of flux to apply aprotective layer to all parts of the assembly; then heating the assemblyto a red heat.

3. The process of bonding a non-ferrous metallic structure of high heatconductivity to a cast iron body, which consists in assembling thenon-ferrous structure and the cast iron body with a thin sheet ofsuitable bonding metal interposed between said structure and said body.and suitable flux between said sheet and structure and between saidsheet and body; then heating the assembly to a red heat while keepingsaid non-ferrous structure and the adjacent surface of the body treefrom contact with products of combustion.

4. The process of bonding a copper structure to a cast iron body, whichconsists in assembling the copper structure and the cast iron body witha layer of suitable bonding metal and suitable flux interposed betweensaid structure and said body; then heating the assembly to a red heatwith the copper structure and adjacent cast iron surtace free fromcontact with products of combustion.

5, The process of bonding a metallic heatdissipating structure to a.cylinder, which consists in assembling the heat-dissipatin structure andthe cylinder with a layer 0 suitable bonding metal and suitable fluxinterposed between said heat-dissipating structure and said cylinder,then heating the assembly to a temperature sufficient to liquefy thebonding metal and form a cohesive bond while constantly rotating theassembly about a substantially horizontal axis.

(5. The process of bonding a heat-dissipating structure to a cylinder,which consists in assembling the heat-dissipating structure and thecylinder with a layer of suitable bonding metal and suitable fluxinterposed between said heat-dissipating structure and said cylinder,then heating the assembly to a temperature sufficient to liquefy thebonding metal while constantly rotating the assembly about asubstantially horizontal axis, then cooling the assembly whilecontinuing to rotate it.

7 The process of bonding a heat-dissipating structure to a cylinderwhich consists in assembling the heat-dissipating structure and thecylinder with a layer of suitable bonding metal and suitable fluxinterposed between said heat-dissipating structure and said cylinder,then heating the assembly to a temperature sufiicient to liquety thebonding metal while constantly rotating the assembly with the axis ofthe cylinder horizontal, around a substantially horizontal axis.

8. The process of bonding a metallic heatdissipating structure to acylinder or the like. which consists in assembling the heatdissipatingstructure and the cylinder with a thin sheet of suitable bonding metalinterposed, a layer of flux between the sheet and the cylinder, andbetween said sheet and said structure; then heating the assembly to atemperature sufiicient to liquefy the bonding metal and form a cohesivebond.

9. The process of bonding a metallic heatdissipating structure to acylinder or the like. which consists in assembling the heatdissipatingstructure and the cylinder with a layer of suitable bonding metal andsuitable flux interposed between said heat-dissipating structure andsaid cylinder, pressing the heat-dissipating structure tightly to saidcylinder. then heating the assembly to a temperature sutiicient toliquefy the bonding metal and form a cohesive bond while still pressingthe heat-dissipating structure to the cylinder.

10. The process of bonding a metallic heat-dissipatingstructure to acylinder or the like, which consists in assembling the lieat-dissipatingstructure and thecylinder with a layer of suitable bonding metal andsuitable flux interposed between said heatdissipating structure and saidcylinder, clamping the heat-dissipating structure to the cylinder bybands of material having a lower coefficient of expansion than theheat-dissipating structure, then heating the .assembly to a temperaturesufiieient to liquefy the bonding metal and form a cohesive bond.

11. The process of forming and bonding a metallic heat-dissipatingstructure to a cylinder or the like. which consists in pleating a thinsheet of high heat-conducting metal so as to form a plurality ofproperly spaced fin loops connected by plane connecting bases, wrappingsaid pleated sheet around the cylinder with an interposed layer ofsuitable bonding metal and suitable flux, temporarily fixing theheat-dissipating structure in place, then heating the assembly to atemperature sufficient to liquefy the bonding metal and form a coherentbond.

12. The process of forming and bonding a metallic heat-dissipatingstructure to a cylinder or the like, which consists in pleating a thinsheet of high hcat-conducting metal so as to form a plurality ofproperly spaced fin loops connected by plane connecting bases, which areseparated from each other, wrapping said pleated sheet around thecylinder so as to bring the separated bases into substantialjuxtaposition with an interposed layer of suitable bonding metal andsuitable flux, temporarily fixing the heat-dissipating structure inplace, then heating the assembly to a temperature suite cient to liquefythe bonding metal and form a coherent bond.

13. The process of forming and bonding a metallic heat-dissipatingstructure to a cylinder or the like, which consists in pleating a thinsheet of high hcat-conducting metal so as to form a plurality ofproperly spaced fin loops connected by plane connecting bases and havingthe inner edges of the side walls thereof inclined toward each other.wrapping said pleated sheet around the cylinder so as to bring theseparated bases into substantialjuxtaposition with an interposed layerof suitable bonding n'ictal and suitable flux, temporarily fixing thehcatdissipating structure in place, then heating the assembly to atemperature sufiicient to liquet'y the bonding metal and form a coherentbond. Y

14. The process of forming and bonding a metallic heat-dissipatingstructure to a cylinder. which consists in pleating a thin sheet of highheat-conducting metal so as to form a plurality of properly spaced finloops connected by plane connecting bases,

wrapping said pleated sheet around the cylinder with an interposed layerof suitable bonding metal and with suit-able flux between said layer andcylinder and said layer and heat-dissipating structure, temporarilysecuring together the assembled parts and heating the. assembly to atemperature suflieient to liquety the bonding metal and form a coherentbond.

15. The process of forming and bonding a heat-dissipating structure to acylinder, which consists in forming a flexible finning structure in astraight length, having fins projecting therefrom. one group of adjacentfins warying in height in such order and degree that when the sheet isbent to form a cylinder the outer edges of the fins of said group willlie substantially in a common plane; wrapping said finning structure.around the cylinder with suitable interposed bonding metal and flux.then heating the assembly to liquct'y the bonding metal and form acoherent bond between the heat-dissipating structure and the cylinder.

16. The process of forming and bonding a heat-dissipating structure to acylinder, which consists in forming a flexible finning structure in astraight length having fins projecting therefrom, at least one group offins being of less height than the others, wrapping said finningstructure around the cylinder with suitable interposed bonding metal andflux, fitting a filler block against the edges of the shorter fins, andtemporari- 1y bonding said heat-dissipating structure and block to thecylinder by metallic bands of lower coefiicicnt of expansion than theheat-dissipating structure, said filler block being of such size andform that said bands contact with the edges of all fins except thosecovered by the block, then heating the assembly sufiiciently to liquefythe bonding material and form a coherent bond.

17. The process of bonding a thin hcat. dissipating structure to acylinder or like body. which consists in assembling the thinheat-dissipating structure and the body with suitable bonding metal andflux. then applying radiant heat to the assembly sufficient to fuse thebonding metal and form a coherent bond while protecting the thinheatdissipating structure and the bonding metal from products ofcombustion and from oxidation.

In testimony whereof I hereto aifix my signature.

CHARLES F. KETTERING.

